This invention relates in general to methods of producing asphalt roofing products and the asphalt product so produced, and in particular to a method of producing roofing shingle coating asphalts from non-coating grade asphalts such as commodity paving asphalts.
Roofing shingle coating asphalts are usually produced by selecting a suitable feedstock asphalt and then processing that asphalt to provide the properties desired for use in a coating asphalt. For example, asphalt feedstocks used to produce coating asphalts for roofing shingles are usually chosen so that they can be air-blown to: 1) raise their softening point so that they maintain their dimensions at high temperatures on a roof; 2) lower their penetration into a range where it allows proper press of granules without becoming too brittle; 3) raise their melt viscosity so that when filler is added the filled coating viscosity is in a range that allows a roofing shingle process to run at high speeds; and 4) create a shingle that will perform over many years on the roof in spite of being exposed to sun, high temperatures and rain.
Historically coating asphalt for roofing shingles has been produced by choosing a special grade of asphalt as the feedstock to the air blowing process in order to meet these properties. These special grades of asphalt were often materials that were softer (higher penetration, lower viscosity) than paving grade asphalt and were often called “roofer's flux”. Unfortunately, these special grades of asphalts that can be air-blown to make coating asphalts are increasingly in short supply and therefore can be costly compared to many other types of asphalts, particularly commodity paving asphalts. A new method that could use non-coating grade asphalts, such as commodity paving asphalts or other asphalts that are harder than the normal special grades of asphalt, to produce quality coating asphalts for roofing such as shingles would be beneficial to the asphalt roofing product business.
Asphalts have been modified with waxes to produce a variety of roofing and industrial products. For example, Chang et al. (U.S. Pat. No. 4,382,989) discloses a roofing asphalt formulation containing oxidized coating grade asphalt, oxidized polyethylene and optionally saturant asphalt and filler. In one embodiment, the asphalt is oxidized to any degree, then unoxidized polyethylene is added, and then the oxidation process is continued to produce the roofing asphalt formulation. In a later improvement Chang et al. (U.S. Pat. No. 4,497,921) added sulfur to stabilize the mix. Janicki (U.S. Pat. No. 4,554,023) claimed a method of making a roofing shingle asphalt by blending bis-stearoylamide wax into asphalt, including blown asphalt, particularly asphalts with 143° F. softening points, with a benefit of lowering the viscosity of the asphalt product. None of these techniques consistently met specifications for roofing shingle coating asphalts and were usable with many asphalts.
There still exists a need for a method of producing coating asphalts for roofing shingles from non-coating grade asphalts such as commodity paving asphalts.